1. Field of the Invention
The present invention relates to the field of engine analysis and control, and more particularly to the field of acquisition of a signal coming from at least one sensor positioned on an engine.
2. Description of the Prior Art
The various applications on engine test benches require acquisition of physical quantities (pressures, temperatures, flow rates, etc.). An engine under test is thus equipped with sensors, each one delivering a voltage or a current in analog form to one or more data acquisition or engine control systems.
Conventionally, the analog signal from the sensor is first conditioned. It therefore generally undergoes voltage conversion, amplification and filtering.
The analog signal obtained is then digitized by means of an analog-to-digital converter delivering samples generally coded at 12, 14 or 16 bits. In the field of engine signal acquisition, that is signals coming from sensors positioned on an engine, the conversion trigger signal depends on the crankshaft rotation and it generally comes from either an angular coder located at the end of the crankshaft, or from an engine target wheel (58X or other) also positioned at the end of the crankshaft. Thus, analog-to-digital conversion of the signals can be carried out every 6 crank angle degrees, every crank angle degree or every 1/10 crank angle degree. The sequence of the various samples obtained is then used to calculate various parameters useful for combustion analysis or engine control. These calculations can be made either on one engine cycle corresponding to one or more crankshaft rotations, or on several engine cycles.
However, some calculations require temporal sampling so as to meet the sampled signal theory. These calculations are based on signal processing algorithms (Fourier transforms, filtering, wavelet transforms, etc.). Noise analysis can be mentioned for example. Thus, the signal coming from a sensor requires two samplings: temporal sampling and sampling synchronized with the engine rotation.
However, it is often necessary, for some calculations such as combustion analysis or TDC (top dead center) calibration, to correlate the temporal position of a sample with the angular position of the crankshaft. This reconstructs, from a temporal acquisition and from a crankshaft rotation signal, the sequence of samples as if they resulted from a sampling synchronized with the crankshaft rotation. This operation currently involves complex sample dating means, whether hardware or software.
The following document describes a technique allowing, by means of calculations, recalibration of or resealing of signals in time:                Laakso T. I. et al, “Splitting the Unit Delay”, in IEEE Signal Processing Magazine, 1996.        
However, this fractional delay (smaller than unity) processing technique describes an ideal filter that cannot be implemented for engine control or test bench applications because its impulse response is infinitely long.